Arboriculture & Urban Forestry 32(4): July 2006 187 Table 5. R2 correlations for fine POM and potential N mineralization and microbial biomass N throughout two growing seasons in urban soils in Moscow, Idaho, and Pullman, Washington, in 2002 and 2003. Potential N mineralization Date 4/17/02 5/01/02 5/15/02 5/29/02 6/12/02 6/26/02 8/07/02 9/05/02 10/03/02 4/11/03 5/09/03 6/13/03 7/11/03 8/08/03 9/13/03 10/10/03 Mean Fine POM kg m−2 0.371 0.325 0.706 0.037* 0.168 0.266 0.737 0.524 0.342 0.537 0.386 0.222 0.628 0.640 0.437 0.575 0.431 *Not significant at the P 0.05. POM, particulate organic matter. explained variance in microbial biomass N (mean R20.73 and 16 of 16 significant) and potential N mineralization (mean R2 0.43 and 15 of 16 significant) (Table 5). In addition, both the carbon and nitrogen contents of the fine POM determined by automated dry combustion were signifi- cantly correlated with MBN and PMN on all dates (Table 6). Seasonal mean values for microbial biomass, carbon miner- alization, and nitrogen mineralization were significantly cor- related with fine POM (Table 7). Fine POM explained much of the variance in seasonal mean microbial biomass nitrogen (R2 values of 0.758 and 0.886) and nitrogen mineralization Table 7. R2 Washington, in 2002 and 2003. Year Measure 2002 2003 Fine POM Microbial biomass N Potential C mineralization Potential N mineralization Fine POM Microbial biomass N Potential C mineralization Potential N mineralization Microbial biomass N Fine POM kg m−2 0.693 0.958 0.531 0.940 0.745 0.595 0.400 0.740 0.966 0.309 0.795 0.651 0.760 0.888 0.919 0.802 0.731 Table 6. R2 correlations for fine POM C and N contents and potential N mineralization and microbial biomass N throughout two growing seasons in urban soils in Moscow, Idaho, and Pullman, Washington, in 2002 and 2003. Potential N mineralization Date Fine POM N 4/17/02 0.496 5/15/02 0.638 6/12/02 0.299 8/07/02 0.670 10/03/02 0.179 4/11/03 0.440 6/13/03 0.183 8/08/03 0.490 10/10/03 0.680 Mean 0.453 Fine POM C 0.477 0.640 0.221 0.803 0.343 0.483 0.274 0.614 0.706 0.507 POM, particulate organic matter. (R2 values of 0.614 and 0.558). Fine POM best related dif- ferences among the urban landscapes that corresponded to differences detected in microbial biomass, carbon mineral- ization, and nitrogen mineralization. Like the soil biologic measurements, fine POM was greater on old residential, park, and street sites compared with new residential and mulch sites. Particulate organic matter may be a practical and accurate nitrogen assessment tool, but measurements are yet to be related to plant productivity and specific nitrogen fertilization recommendations. Our data show that fine POM corresponds to a rate of soil nitrogen mineralization, which could be used to calculate the potential amount of available nitrogen over a growing season. Before prescription fertilization can adopt a POM measurement, more data need to be collected from a wider range of urban soils relating POM with available soil nitrogen, fertilization, and plant performance. correlations among fine POM and microbial measures in urban soils in Moscow, Idaho, and Pullman, Fine POM Microbial biomass N Potential C mineralization 1.000 0.126 1.000 0.300 Potential N mineralization 1.000 —— — 0.758 0.422 0.614 1.000 —— 0.132 0.686 — 1.000 1.000 —— — 0.886 0.431 0.558 1.000 —— 0.335 0.733 — 1.000 All correlations significant at P 0.05. Each value is the mean of 9 or 7 sample dates (2002 and 2003, respectively), with four plots per type, two subplots per plot, for a total of 72 (2002) and 56 (2003). POM, particulate organic matter. ©2006 International Society of Arboriculture Microbial biomass N Fine POM N 0.565 0.509 0.743 0.195 0.854 0.181 0.486 0.637 0.540 0.523 Fine POM C 0.654 0.643 0.781 0.319 0.956 0.301 0.667 0.811 0.532 0.629
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